In case of continuous beam /girder bridges the end span is kept 80% of internal span. This span arrangement leads to uniform sagging momnet in mid span compared to sagging momment obtained in all equal span arrangement. Figure 1 shows bending moment diagram for two span arrangement, a) Last span equal to 0.8 times internal span b) All spans equal under uniformly distributed load.
One of bridge designed in Middle East had span arrangement of 40m - 50m - 50m -40m and this arrangement lead to uniform depth of box girder with least consumption of post-tenisoned tendon.
Figure 1 Bending Moment Diagram for uniformly distributed load on all four spans
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